A carbon dioxide removal system maintains carbon dioxide (CO2) concentration at a safe level. Maintaining CO2 at safe levels can be accomplished by passing exhaled gases through a chemical adsorbent, such as soda lime or anhydrous lithium hydroxide (LiOH). The cartridge is composed of fine adsorbent powder formed into a microporous sheet by thermally induced phase separation of polyethylene. The process to produce sheets of microporous lithium hydroxide/calcium hydroxide is defined in U.S. Pat. No. 5,964,221. This technology of forming fine powders into pliable sheets replaced the older technology of forming adsorbent powders into granular adsorbents. Both microporous lithium hydroxide and calcium hydroxide adsorbents can be produced under the original patent. The wound cartridge product corrects may of the problems associated with granular adsorbents, such as dusting, settling, flow channeling and high pressure drop.
The microporous technology has been deployed in rebreather systems, mine shelters, and unpowered emergency carbon dioxide control in submarines. Submarines use pre-filled cartridges of granular adsorbents for routine, non-emergency, carbon dioxide control. Pre-packed containers of adsorbent are installed into an electric powered canister system for scrubbing CO2. These pre-packed granules rely on a relatively large container (or exoskeleton) to hold the granules. The plastic exoskeleton containers add material cost to the adsorbent manufacture. They also may pose safety hazards by increasing the amount of available fuel in the event of a fire. Plastic containers also have an environmental impact associated with their disposal. As an alternative, reusable, pre-packed metal containers are easy to handle, safe in a fire and do not contribute to landfills; however in submarine applications for example, they are more expensive initially, and there is a larger logistics cost for handling and off-hull refilling of spent cartridges of adsorbent. The system of stacking adsorbent sheets into a rectangular pack (as described in U.S. Pat. No. 5,964,221) is both costly and inefficient. The bulky external frame required to support the sheets occupies volume and adds manufacturing cost. In applications such as space craft and submarines volume is a primary design driver.
An alternative to adsorbent cartridges with rigid frames is the ExtendAir® adsorbent cartridge manufactured by Micropore Inc. For many applications, an adsorbent sheet is wound on a cylindrical core. The adsorbent is prevented from unwinding, using an inexpensive polymer film wrapped around the outside of the cartridge. This wound cartridge does not require an expensive, and bulky external housing (exoskeleton) to maintain its shape. The parallel adsorbent surfaces are held in contact with each other by the tension applied during the winding process and maintained by the outer polymer film wrap. This cartridge has the ease of handling advantages but the cylindrical geometry is inefficient for storage volume and scrubber installation.
This invention addresses these needs and others.